This thesis investigates the variation between null and overt pronouns in subject position in Catalan, a null subject language. I argue that null and overt subject pronouns are two resources that speakers efficiently deploy to signal their intended interpretation regarding antecedent choice or semantic meaning, and that communicative agents interact strategically in order to communicate the desired meaning with the most economical form possible. The mathematical framework of Game Theory is used to analyze this variation, since it is particularly suitable for modeling strategic interaction and choices.

The Position of Antecedent Hypothesis, proposed by Carminati (2002) for Italian, states that null pronouns have a subject preference, while overt pronouns have a non-subject preference. I show that Catalan intersentential data conforms to the PAH whenever the subject is the link of the sentence. However, the PAH needs to be redefined once the topic-focus articulation of the sentence is taken into account: null pronouns have a subject preference regardless of whether the subject is acting as link of the sentence or not, while overt pronouns have a preference for low salience (non-subject, non-link) antecedents. These results point to a model in which salience is composed of several factors and different forms are sensitive to different factors. This data is modeled using games of partial information, in which information states represent different levels of salience. This model makes the prediction that the biases emerging from the PAH should be overridden if there are powerful enough contextual cues, which is borne out.

The relative rates of null and overt pronouns vary greatly in different Romance varieties. I present two hypotheses to deal with this variation: one based on priming effects and the other on a grammatical change in progress. Finally, the relationship between contrastivity and overt pronouns is addressed. I argue that all instances of contrastive pronouns are Contrastive Topic markers, which trigger an uncertainty contrast interpretation, which can be coerced into an exhaustive contrast if there is a salient alternative in the discourse or in the context. I offer a game theoretical analysis of the pairing between forms and contrastive meanings.